The present invention relates to particulate, expandable polymer which can be processed into a foam having a fine cell structure and a low density and which, in order to improve the thermal insulation value thereof, contains a carbon-based thermal-insulation-value-increasing material. The present invention further relates to a method for preparing particulate, expandable polymer as well as to a foam material obtained therewith.
From European patent EP 1 486 530 (corresponding to NL 1023638) in the name of the present applicant expandable polystyrene (EPS) is known in which active carbon is present in the polystyrene particles as a thermal-insulation-value-increasing material. The active carbon that is used has a particle size of <12 microns. A foam obtained by using such a thermal insulation value increasing-material complies with the fire-resistance requirements according to the B2 test, viz. DIN 4101 part 2.
From WO 2010/041936 in the name of the present applicant expandable polystyrene (EPS) is known in which active carbon exhibiting a specific particle distribution is used as a thermal insulation value-increasing material.
From U.S. Pat. No. 6,130,265 a method for preparing graphite-containing EPS is known in which an amount of 0.05-25 wt. % graphite, based on the amount of styrene polymer, is added.
From U.S. Pat. No. 6,340,713 a particulate, expandable polystyrene is known, which styrene polymer comprises 0.05-8 wt. % homogeneously distributed graphite particles having an average particle size of 1-50 μm.
A method for increasing the thermal insulation value of EPS is furthermore known per se from International patent application WO 00/43442, in which styrene polymer is melted in an extruder and mixed with at least a blowing agent and aluminium particles, which are mainly in the form of platelets, and jointly extruded, with the amount of aluminium particles being used being at most 6 wt. %, whereupon the extrudate is cooled and reduced into particles. Such polymers contain at least aluminium in the form of particles so as to improve the thermal insulation properties thereof, which aluminium particles are homogeneously distributed and incorporated as a material that reflects infrared radiation. The aluminium particles have a platelet-like shape, whose dimensions vary from 1 to 15 μm.
The starting material that is used for producing expandable polystyrene (EPS) can be obtained not only via the extrusion process as known from the aforesaid international patent application, but also via suspension polymerisation. The EPS granulate thus obtained is generally used as a starting material in the packaging industry and in the construction industry. The method for the further processing comprises a pre-foaming treatment, in which an amount of steam is passed through a layer of EPS granules in an expansion vessel, as a result of which the blowing agent present in the EPS granules, usually pentane, is evaporated and foaming of the granules takes place. After a storage period of approximately 4-48 hours, also referred to as “maturing”, the thus pre-foamed granule is introduced into a mould, in which the granules are further expanded under the influence of steam. The mould used in that process is provided with small openings through which the blowing agent that is still present can escape whilst the granules fuse to the desired shape. The dimensions of said shape are in principle not bound by limitations, making it possible to produce blocks for use in the construction industry as well as packaging materials for food products and non-food products.